Plasmonics has established itself as a branch of physics which, among other applications, has the potential to revolutionize data processing, improve photovoltaics, and increase sensitivity of bio-detection. Plasmonics generally relates to the interaction between light and electron plasma oscillations in metals. Surface plasmons are coherent oscillations of free electrons that exist at an interface between two materials where the real part of the dielectric function changes sign across the interface (e.g. a metal-dielectric interface).
Gold is the current metal of choice for plasmonic applications due to its strong plasmonic response. However, gold is not compatible with standard silicon manufacturing processes (e.g. complementary metal oxide semiconductor (CMOS) technology) due to an efficient diffusion of gold into silicon. This incompatibility, together with the relatively high cost of gold, has hindered the widespread use and adoption of plasmonic devices.
There is an on-going search for inexpensive alternative materials that may replace gold for plasmonic applications and make plasmonic devices more economically attractive.
In one numerical (i.e. theoretical) study (Choi et al; Graphene-on-silver substrates for sensitive surface plasmon resonance imaging biosensors. Optics Express, 17 Jan. 2011, Vol. 19, No. 2, 458) it is hypothesized that a silver film coated in graphene may improve the sensing performance of a silver-based surface plasmon resonance (SPR) imaging biosensor beyond that of an equivalent gold-based SPR imaging biosensor. However, experimental attempts to date have not resulted in a device that possesses the desired plasmonic response required to make a functional plasmonic device. As an example, Salihoglu et al. (Plasmon-polaritons on graphene-metal surface and their use in biosensors. Applied Physics Letters, 23 May 2012, vol. 100, 213110) reports an experimental attempt to use graphene coated silver for use in a plasmonic device. However, it was found that the addition of the graphene to the silver significantly degraded the plasmonic response of the material.
There still exists a need, therefore, for alternative plasmonic structures that will enable commercially viable plasmonic devices.
It is an aim of certain embodiments of the present invention to provide a plasmonic structure that is resistant to oxidation.
Another aim of certain embodiments of the present invention is to provide a plasmonic structure that may function in a wet environment.
A further aim of certain embodiments of the present invention is to provide a plasmonic structure that is compatible with complementary metal oxide semiconductors (CMOS) and CMOS fabrication methods.
It is also an aim of certain embodiments of the present invention to provide a plasmonic structure that is functionalized for biological applications.
Another aim of certain embodiments of the present invention is to provide a plasmonic structure that is convenient and/or inexpensive to manufacture.
The present invention satisfies some or all of the above aims.